Scientists have discovered what causes cataclysm-inducing supervolcanoes to erupt, and the answer offers little reassurance. Their eruptions are caused by magma buoyancy, which makes them less predictable and more frequent than previously thought.

A team of geologists from the Swiss Federal Institute of Technology in Zurich (ETH) modeled a supervolcano – such as Yellowstone in Wyoming – using synthetic magma heated up with a high-energy X-ray to see what could create a powerful discharge. A separate international team, led by Luca Caricchi of the University of Geneva, conducted more than 1.2 million computer simulations of eruptions.

Both groups have arrived at similar conclusions, with twostudies simultaneously published in Nature Geoscience magazine.

"We knew the clock was ticking but we didn't know how fast: what would it take to trigger a super-eruption?” said Wim Malfait, the lead author of the ETH study.

"Now we know you don't need any extra factor - a supervolcano can erupt due to its enormous size alone.”

It was previously thought that supervolcanoes – which spew out hundreds more times of lava and ash than ordinary ruptures – could be triggered by earthquakes or other outside tectonic phenomena.

It was also clear that these volcanoes do not operate like ordinary eruptions, which rely on magma filling their chambers, and spurting through an opening, once the pressure gets to a certain point, since the chambers of supervolcanoes are too large to be over pressurized to the same degree.

Now, the studies have identified the unique supervolcano mechanism that makes their discharge more like powerful explosions than normal eruptions.

The molten magma in the mostly underground supervolcano is lighter than the surrounding rocks, and the difference in pressure, creates a 'buoyancy effect', meaning the super-hot terrestrial soup is always attempting to burst out.

“The difference in density between the molten magma in the caldera and the surrounding rock is big enough to drive the magma from the chamber to the surface,” said Jean-Philippe Perrillat of the National Centre for Scientific Research in Grenoble, where the experiments were conducted.

Artist's impression of the magma chamber of a supervolcano with partially molten magma at the top. (ESRF/Nigel Hawtin)

“The effect is like the extra buoyancy of a football when it is filled with air underwater, which forces it to the surface because of the denser water around it. If the volume of magma is big enough, it should come to the surface and explode like a champagne bottle being uncorked.”

The researchers believe that the pressure force of the molten magma pools can be strong enough to crack 10 km thick layers of rock, before spewing out a maximum of between 3,500 and 7,000 cubic kilometers of lava. In comparison, the notorious Krakatoa explosion in 1883 likely ejected less than 30 cubic kilometers of debris into the atmosphere.

The effects on Earth are likely to be fundamental, with previous studies suggesting that such a supervolcano could decrease the temperature on Earth by 10 C for a decade, as the ash would prevent sunlight from reaching the ground.

The last supervolcano eruption in Lake Toba took place more than 70,000 years ago. According to one highly-contested theory it may have wiped out more than half of the planet’s population; in any case the effect on the world would be dramatic.

"This is something that, as a species, we will eventually have to deal with. It will happen in future," said Dr Malfait.

"You could compare it to an asteroid impact - the risk at any given time is small, but when it happens the consequences will be catastrophic."

A volcano has to eject more than 1,000 cubic km of debris in a single eruption to be counted as a supervolcano, and there are less than ten potential sites with sufficiently large magma chambers around the world, though there may be others lurking underneath the ocean surface. These formations, which are more often flat with no outlet, are expected to erupt once every 50,000 years, though there is no regularity to the frequency of eruptions.

The computer modelers believe that the buoyancy mechanism means that such eruptions occur more frequently than previously thought, though the exact extent is hard to estimate without studying magma flows at each potential location.

Nonetheless, the ETH scientists say that there could be detectable pressure changes, and perhaps even spectacular rises of ground level sometime before the eventual explosion. But it is not clear how long after such changes an eruption would take place, or whether advance knowledge would actually help to mitigate its impact.

A supervolcano beneath Yellowstone National Park is larger than originally thought and one that could wipe out global civilizations after researchers were able to map its massive volcanic chamber.

New research shows that Yellowstone's magma chamber is at least 250 percent larger than previously believed with the chamber being roughly 55 miles by 20 miles. The eruption produced by such a large volcano would drastically alter the Earth's climate leading to mass die-offs of species around the world.

"We've been working there for a long time, and we've always thought it would be bigger ... but this finding is astounding," University of Utah Professor Bob Smith recently told BBC News.

Geophysicists and geologists have been trying to determine the exact size of the volcanic chamber of some years now and after new developments in research technologies and methods combined with a recent series of small earthquakes were able to map and get a more precise measurement of the volcanic chamber.

"We know there's been these really large volcanic eruptions in the past and what we're seeing now matches that," Dr. Jamie Farrell told BBC News, adding that when the volcano underneath Yellowstone does erupts it will be 2,000 times larger than the eruption of Mount St. Helens in 1980.

According to the U.S. Geological Survey there were more than 300 earthquakes that hit the region around Yellowstone National Park in the month of November alone.

Still, geologists contend that the makeup of the magma and the surrounding rock of the Earth's crust will combine for an explosive eruption.

"The difference in density between molten magma in the caldera and the surrounding rock is big enough to drive magma from the chamber to the surface," Dr. Jean-Philippe Perrillat, of the National Centre for Scientific Research in Grenoble, said in a statement

"The effect is like the extra buoyancy of a football when it is filled with air underwater, which forces it to the surface because of the denser water around it," Perrillat said. "If the volume of magma is big enough, it should come to the surface and explode like a champagne bottle being uncorked."

Grenoble - An independent ball of magma, pressurized to 36,000 atmospheres, has been identified under Yellowstone. The magma is said to be able to erupt “without any external trigger”.

That not-quite-cryptic-enough expression means the caldera can blow under its own steam, if you’ll excuse the expression, without interaction with other forces. It’s not dependent on feeds of magma from the mantle or earthquakes to detonate, for example.

Scientists have analysed magma from the Yellowstone caldera, a 55-mile-wide underground cavern containing between 200 and 600 cubic kilometres of molten rock, to see how it responds to changes in pressure and temperature.

“The difference in density between the molten magma in the caldera and the surrounding rock is big enough to drive the magma from the chamber to the surface,” said Jean-Philippe Perrillat of the National Centre for Scientific Research in Grenoble.

Kelvin Case

Yellowstone National Park actually sits on top of four over-lapping calderas.

While a lot of gruesome fiction has been produced on the subject of super volcanoes, the known facts about "ordinary" volcanoes are terrifying enough:

1. In 535 AD, dendochronologists note an almost total absence of growth in tree rings in Ireland believed to be caused by volcanic eruptions in Indonesia. The sunlight was blocked, “like an eclipse”, according to ancient records. Fogs were reported in the Middle East, and crop failures caused famine.

QUESTION: Do scientists know if a catastrophic eruption is currently imminent at Yellowstone?

ANSWER: There is no evidence that a catastrophic eruption at Yellowstone is imminent, and such events are unlikely to occur in the next few centuries. Scientists have also found no indication of an imminent smaller eruption of lava.

QUESTION: How far in advance could scientists predict an eruption of the Yellowstone volcano?

ANSWER: The science of forecasting a volcanic eruption has significantly advanced over the past 25 years. Most scientists think that the buildup preceding a catastrophic eruption would be detectable for weeks and perhaps months to years. Precursors to volcanic eruptions include strong earthquake swarms and rapid ground deformation and typically take place days to weeks before an actual eruption. Scientists at the Yellowstone Volcano Observatory (YVO) closely monitor the Yellowstone region for such precursors. They expect that the buildup to larger eruptions would include intense precursory activity (far exceeding background levels) at multiple spots within the Yellowstone volcano. As at many caldera systems around the world, small earthquakes, ground uplift and subsidence, and gas releases at Yellowstone are commonplace events and do not reflect impending eruptions.

The USGS calculates the odds against an eruption as “730,000 to 1” on a yearly basis.

Scenarios- What a really big eruption might do

The probability of the entire magma field erupting is the worst case scenario. At a pressure of 36,000 atmospheres, the best analogy is a major nuclear strike. The result of a major detonation would be to displace an enormous volume of air, with massive shock waves. Depending on the physical values of the pressure of the waves and atmospheric pressures, both displaced and on impact, the direct effects of the blast could be felt across America. The atmosphere will also rush back in, like after a high explosive detonation, a double whammy.

Air pressures alone in both events could be catastrophic.

(At a pressure of 2 atmospheres, even balance and hearing can be affected. At multiple atmospheres, anything is possible. The range of effects depends on how much energy is transferred into the atmosphere during the detonation and the recoil of the atmosphere. An analogy would be deep water diving, “instant bends” caused by atmospheric pressures.

The Rockies would provide some shielding from the blast to the west, but the plains, north east and south would take an almost unrestricted blast. The inrush of returning winds after the explosion could be at hurricane force intensity, regardless of mountain ranges. Like Mt. St. Helens, but on an infinitely larger scale, the air pressure alone could flatten forests and anything else they hit.

Pyroclastic flows: These are caused when rock and materials vaporize. They’re a combination of these materials and gases, and are like 100 mph flame throwers racing along the ground surface, obliterating everything in their way. Pyroclastic flows caused the Pompeii disaster, as well as St. Pierre. Very large pyroclastic flows could annihilate areas around the eruption site.

Radiant heat would cover a large area around the caldera at lava temperatures, approximately 700-1200C. This would be a “local event” of several hundred square miles.

Tectonic effects: Unknown. An eruption would at least cause local earthquakes. In theory, the movement of large amounts of rock should affect tectonic dynamics to some degree, but it’s really guesswork.

The worst effects, ironically, would be after the explosion. Climate disruption would be inevitable, and the toxic materials deposited by a super volcano could spread around the world, as sulfates from major volcanoes are believed to have done in prior eruptions.

Large amounts of ash in the atmosphere could block sunlight, globally, as in prior examples. Crop failure and pollution through microparticulates could be extremely serious. Respiratory effects would be inevitable, a sort of “global asthma” possible at a certain range of parts per million in the atmosphere. Contamination of dams and reservoirs would be a likely scenario.

Blocking photosynthesis could also add serious problems in terms of the global environment. Super volcanoes are believed responsible for previous mass extinctions, and it’s not hard to see why. Crashing the various environmental cycles, like the water, carbon, nitrogen cycles, could disrupt a wide range of biological processes.

Microbiological processes are also likely to be severely disrupted in the blast area and highly reactive in areas affected by chemical processes from the volcanic materials.

The good news, such as it is, is that Yellowstone’s dynamics don’t seem prone to explosive events. The magma seems comparatively stable. Sporadic lava flows are much more likely. The new information has added another element to the puzzle, but not a basis for prediction.

The grey area is that while the current situation appears stable, what happens if more materials are added from the mantle, or a change to the chemical/gas mix appears in the caldera? Let’s hope we don’t find out. 36,000 atmospheres is a lot of pressure. At that pressure, a gas cylinder, let alone a super volcano, would create a massive explosion. If that blows, dig a hole and hope for the best.